System and method for estimating photovoltaic energy through irradiance to irradiation equating with the aid of a digital computer
The accuracy of photovoltaic simulation modeling is predicated upon the selection of a type of solar resource data appropriate to the form of simulation desired. Photovoltaic power simulation requires irradiance data. Photovoltaic energy simulation requires normalized irradiation data. Normalized irradiation is not always available, such as in photovoltaic plant installations where only point measurements of irradiance are sporadically collected or even entirely absent. Normalized irradiation can be estimated through several methodologies, including assuming that normalized irradiation simply equals irradiance, directly estimating normalized irradiation, applying linear interpolation to irradiance, applying linear interpolation to clearness index values, and empirically deriving irradiance weights. The normalized irradiation can then be used to forecast photovoltaic fleet energy production.
1. A system for estimating photovoltaic energy through irradiance to irradiation equating with the aid of a digital computer, comprising:
at least one computer processor configured to:
provide with a set of irradiance observations that have been recorded for a location at which a photovoltaic plant can be operated with each irradiance observation in the set being separated by regular intervals of time;
provide with a set of clear sky irradiance with each clear sky irradiance in the set corresponding to one of the irradiance observations;
estimate a set of normalized irradiation with each normalized irradiation estimates in the set corresponding to one of the irradiance observations, wherein each of the normalized irradiation estimates is equal to one of the irradiation observations;
form a time series of clearness indexes with each clearness index in the time series corresponding to one of the irradiance observations, each clearness index comprising a ratio of the irradiance observation's corresponding normalized irradiation estimate and the irradiance observation's corresponding clear sky irradiance; and
forecast photovoltaic energy production for the photovoltaic plant in the computer as a function of the time series of the clearness indexes and photovoltaic plant's power rating.
2. A system according to claim 1 , wherein each normalized irradiation estimate is associated with a time period, wherein a plurality of the irradiance observations are associated with that time period, and wherein the one irradiance observation is closer than remaining ones of the irradiance observations to a middle of the time period associated with the normalized irradiation estimate equal to the one irradiance observation.
3. A system according to claim 1 , the at least one processor further configured to:
plot the irradiance observation on a graph; and
identify the one irradiance observation based on the graph.
4. A system according to claim 1 , wherein the photovoltaic fleet is integrated into a power grid and wherein the power grid is operated based on the forecast photovoltaic energy production for the photovoltaic fleet.
5. A system according to claim 1 , the at least one processor further configured to:
collect raw irradiance observations from a plurality of ground-based weather stations; and
assemble the irradiance observations as point statistics, each comprising an average of all values of the raw irradiance observations.
6. A system according to claim 1 , the at least one processor further configured to:
collect a time series of power statistics from a plurality of existing photovoltaic stations;
select a performance model for each of the existing photovoltaic stations and inferring apparent irradiance as area statistics based on the performance model selected and the time series of power statistics; and
determine the irradiance observations as average point statistics, each comprising an average of all values of the apparent irradiance.
7. A system according to claim 1 , the at least one processor further configured to:
collect area solar irradiance statistics, each comprising a set of pixels from satellite imagery for a physical area within the geographic region;
convert the area solar irradiance statistics to irradiance statistics for an average point within the set of pixels; and
determine the irradiance observations as average point statistics, each comprising an average of all values of the set of pixels.
8. A system according to claim 1 , wherein the at least one processor is comprised in a distributed processing topology.
9. A system according to claim 4 , the at least one processor further configured to:
provide the forecast photovoltaic energy production to at least one of a planner and an operator of the power grid.
10. A system according to claim 4 , wherein the power grid comprises transmission and distribution infrastructure that delivers the produced energy to consumers.
11. A method for estimating photovoltaic energy through irradiance to irradiation equating with the aid of a digital computer, comprising the steps of:
providing at least one computer with a set of irradiance observations that have been recorded for a location at which a photovoltaic plant can be operated with each irradiance observation in the set being separated by regular intervals of time;
providing the at least one computer with a set of clear sky irradiance with each clear sky irradiance in the set corresponding to one of the irradiance observations;
estimating a set of normalized irradiation in the at least one computer with each normalized irradiation estimates in the set corresponding to one of the irradiance observations, wherein each of the normalized irradiation estimates is equal to one of the irradiation observations;
forming a time series of clearness indexes in the at least one computer with each clearness index in the time series corresponding to one of the irradiance observations, each clearness index comprising a ratio of the irradiance observation's corresponding normalized irradiation estimate and the irradiance observation's corresponding clear sky irradiance; and
forecasting by the at least one computer photovoltaic energy production for the photovoltaic plant as a function of the time series of the clearness indexes and photovoltaic plant's power rating.
12. A method according to claim 11 , wherein each normalized irradiation estimate is associated with a time period, wherein a plurality of the irradiance observations are associated with that time period, and wherein the one irradiance observation is closer than remaining ones of the irradiance observations to a middle of the time period associated with the normalized irradiation estimate equal to the one irradiance observation.
13. A method according to claim 11 , further comprising:
plotting the irradiance observation on a graph; and
identifying the one irradiance observation based on the graph.
14. A method according to claim 11 , wherein the photovoltaic fleet is integrated into a power grid and wherein the power grid is operated based on the forecast photovoltaic energy production for the photovoltaic fleet.
15. A method according to claim 11 , further comprising:
collecting raw irradiance observations from a plurality of ground-based weather stations; and
assembling the irradiance observations as point statistics, each comprising an average of all values of the raw irradiance observations.
16. A method according to claim 11 , further comprising:
collecting a time series of power statistics from a plurality of existing photovoltaic stations;
selecting a performance model for each of the existing photovoltaic stations and inferring apparent irradiance as area statistics based on the performance model selected and the time series of power statistics; and
determining the irradiance observations as average point statistics, each comprising an average of all values of the apparent irradiance.
17. A method according to claim 11 , further comprising:
collecting area solar irradiance statistics, each comprising a set of pixels from satellite imagery for a physical area within the geographic region;
converting the area solar irradiance statistics to irradiance statistics for an average point within the set of pixels; and
determining the irradiance observations as average point statistics, each comprising an average of all values of the set of pixels.
18. A method according to claim 11 , wherein the at least one computer is comprised in a distributed processing topology.
19. A method according to claim 14 , further comprising:
providing the forecast photovoltaic energy production to at least one of a planner and an operator of the power grid.
20. A method according to claim 14 , wherein the power grid comprises transmission and distribution infrastructure that delivers the produced energy to consumers.